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PDCA (plan-do-check-act) is an iterative four-step problem-solving process typically used in business process improvement. It is also known as the Deming cycle, Shewhart cycle, Deming wheel, or plan-do-study-act.



The PDCA cycle
Establish the objectives and processes necessary to deliver results in accordance with the expected output. By making the expected output the focus, it differs from other techniques in that the completeness and accuracy of the specification is also part of the improvement.
Implement the new processes. Often on a small scale if possible.
Measure the new processes and compare the results against the expected results to ascertain any differences.
Analyze the differences to determine their cause. Each will be part of either one or more of the P-D-C-A steps. Determine where to apply changes that will include improvement. When a pass through these four steps does not result in the need to improve, refine the scope to which PDCA is applied until there is a plan that involves improvement.


PDCA was made popular by Dr. W. Edwards Deming, who is considered by many to be the father of modern quality control; however it was always referred to by him as the "Shewhart cycle." Later in Deming's career, he modified PDCA to "Plan, Do, Study, Act" (PDSA) so as to better describe his recommendations.

The concept of PDCA is based on the scientific method, as developed from the work of Francis Bacon (Novum Organum, 1620). The scientific method can be written as "hypothesis" - "experiment" - "evaluation" or plan, do, and check. Shewhart described manufacture under "control" - under statistical control - as a three step process of specification, production, and inspection.[1] He also specifically related this to the scientific method of hypothesis, experiment, and evaluation. Shewhart[2] says that the statistician "must help to change the demand [for goods] by to close up the tolerance range and to improve the quality of goods." Clearly, Shewhart intended the analyst to take action based on the conclusions of the evaluation. According to Deming[3] during his lectures in Japan in the early 1950's the Japanese participants shortened the steps to the now traditional plan, do, check, act. Deming preferred plan, do, study, act because "study" has connotations in English closer to Shewhart's intent than "check."

A fundamental principle of the scientific method and PDSA is iteration - once a hypothesis is confirmed (or negated), executing the cycle again will extend the knowledge further. Repeating the PDSA cycle can bring us closer to the goal, usually a perfect operation and output.

In Six Sigma programs, the PDSA cycle is called "define, measure, analyze, improve, control" (DMAIC). The iterative nature of the cycle must be explicitly added to the DMAIC procedure.

PDSA should be repeatedly implemented in spirals of increasing knowledge of the system that converge on the ultimate goal, each cycle closer than the previous. One can envision an open coil spring, with each loop being one cycle of the Scientific Method - PDSA, and each complete cycle indicating an increase in our knowledge of the system under study. This approach is based on the belief that our knowledge and skills are limited, but improving. Especially at the start of a project, key information may not be known; the PDSA - scientific method - provides feedback to justify our guesses (hypotheses) and increase our knowledge. Rather than enter "analysis paralysis" to get it perfect the first time, it is better to be approximately right than exactly wrong. With the improved knowledge, we may choose to refine or alter the goal (ideal state). Certainly, the PDSA approach can bring us closer to whatever goal we choose.

Rate of change, that is, rate of improvement, is a key competitive factor in today's world. PDSA allows for major 'jumps' in performance ('breakthroughs' often desired in a Western approach), as well as Kaizen (frequent small improvements associated with an Eastern approach). In the United States a PDSA approach is usually associated with a sizable project involving numerous people's time, and thus managers want to see large 'breakthrough' improvements to justify the effort expended. However, the Scientific Method and PDSA apply to all sorts of projects and improvement activities.

The power of Deming's concept lies in its apparent simplicity. The concept of feedback in the Scientific Method, in the abstract sense, is today firmly rooted in education. While apparently easy to understand, it is often difficult to accomplish on an on-going basis due to the intellectual difficulty of judging one's proposals (hypotheses) on the basis of measured results. Many people have an emotional fear of being shown "wrong," even by objective measurements. To avoid such comparisons, we may instead cite complacency, distractions, loss of focus, lack of commitment, re-assigned priorities, lack of resources, etc.

See also


  1. ^ Shewhart (1939), p. 45
  2. ^ Shewhart (1939), p. 48
  3. ^ Deming, p. 88


Further reading

External links



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary





PDCA (uncountable)

  1. the cycle of Plan-Do-Check-Act, four-step solving process typically used in quality control.



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